Combining and Selecting Resistor and Capacitor Values on op-amps

Combining and Selecting Resistor and Capacitor Values on op-amps

Combining Op-Amp StagesCombining op-amp stages to save money and board space is possible in some cases, but itoften leads to unavoidable interactions between filter response characteristics, offset voltages,noise, and other circuit characteristics. The designer should always begin by prototypingseparate gain, offset, and filter stages, then combine them if possible after each individual circuitfunction has been verified. Unless otherwise specified, filter circuits included in this documentare unity gain.

Combining and Selecting Resistor on OP-AMP

Selecting Resistor and Capacitor ValuesThe designer who is new to analog design often wonders how to select component values.Should resistors be in the 1-ohm decade or the 1-Mohm decade? Resistor values in the 1-kohm to100-kohm range are good for general-purpose applications. High-speed applications usually useresistors in the 100-ohm to 1-kohm decade, and they consume more power. Portable applicationsusually use resistors in the 1-Mohm or even 10-Mohm decade, and they are more prone to noise.Basic formulas for selecting resistor and capacitor values for tuned circuits are given in thevarious figures. For filter applications, resistors should be chosen from 1% E-96 values (seeAppendix A). Once the resistor decade range has been selected, choose standard E-12 valuecapacitors. Some tuned circuits may require E-24 values, but they should be avoided wherepossible. Capacitors with only 5% tolerance should be avoided in critical tuned circuits—use 1%instead.